This paper on Spanish for Science and Technology (SST) analyzes the rhetorical functions carried out by the selection of voice — active, passive or se-passive — in five biological research articles in Spanish. It compares these rhetorical functions with those found in French and English scientific papers. Finally it suggests that there may be some universals which can be established on the basis of this comparison, but only through the introduction of an intermediate level of “discourse function” between the levels of rhetorical function and the level of grammatical form.